Radio communication system



May 24, 1949 E.,H. B. BARTELINK l 2,471,138

RADIO COMMUNICATION SYSTEM Filed Aug. 16, 1946 2 Sheets-Sheet 1 NO .I

Lize/9 Nien C -rml.-..J-L J g* www am H i s Attorrwe y May24, 1949. E.H.B.BARTE| 1NK iv 2,471,138

RADIO COMMUNICATION SYSTEM Filed Aug. 1e, 194e v 2 sheets-sheet 2 b 4| 4[ '1 Fi g2. Q Q

d J- I j e j J' l a n J j b J I' 1 I1 Il 1 C Flcg. d j l f l e J J F' .5. ,70 -lg w/s aA/vo HXED FREQUENCY TUNER Alva oen-oma AMPLJF/ER l Inventor.' v

Everhard HExBartel in k,-

H i s Attorney.

Patented May 24, T949 UNITED STATES ATENr oFFlcs signor to General Electric Company,

tion of New York Application August 16, 1946, Serial No. 690,864

(Cl. Z50-9) Claims.

My invention relates to systems of radio communication and more particularly to pulse systems of radio communication.

This application is a continuation in part of my copending application Serial No. 477,496, led March 1, 1943, now abandoned.

Pulse communication systems are advantageous for the transmission of speech, music, and other forms of intelligence, because the effects of extraneous electric elds, noise, etc., which may effect the receiving apparatus, may be reduced. For example, by modulating the frequency or duration of the transmitted pulses of radio frequency carrier, limiting means may be employed to eliminate or at least substantially reduce the amount of noise voltage appearing on the received pulses. It is, therefore, an object of my invention to provide a new and improved radio communication system of the pulse' type.

In conventional radio communication systems, different signal channels are selected by the selection of frequency bands or in other words by tuning to the carrier frequency to be received. It is another object of my invention to provide a system of modulated pulse transmission in which signal selection is made on a time basis rather than a frequency basis, thereby enabling the use of receivers of a much simpler and less expensive type than the conventional type of receiver and yet provide excellent selectivity, frequency response, and low noise level.

In the proposed pulse transmission system several audio channels are substantially simultaneously transmitted over a common wide band radio frequency channel. Each audio channel modulates a group of short duration substantially square pulses. The modulation of the pulses may be modulation of amplitude, frequency, or width.

The pulses are transmitted without mutual interference by using the same repetition rate for each audio signal and by interspersing the pulses of one channel in the intervals between the pulses corresponding to the other audio channels. In the receiver, means is provided for selecting the desired one of the channels and synchronizing the operation of the receiver with that channel.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, both as to its organization and manner oi operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a diagram partly schematic and partly in block form illustrating one form of a transmitting system embodying the principles of my invention; Figs. 2, 3, and 4 are diagrams illustrating the operation of the transmitter illustrated in Fig. 1; and Figs. 5 and 6 are embodiments of receivers adapted to receive the signals transmitted from a, transmitter such as that shown in Fig. 1. In Figs. 1 and l5 pulse shapes at different locations in the circuit are indicated.

In Fig. 1 there is illustrated a system for transmitting ve different signals or audio channels within a single frequency band. There are shown ve multivbrators I0, Ilia, Illb, IIic and Id arranged in cascade so that one multivibrator triggers the next, etc., in order that pulses will be developed in a definite sequence. While multivibrators are shown as pulse generators, any suitable pulse sources may be substituted.

Each multivibrator comprises a pair of electron discharge devices II and I2 including anodes I3 and I4, respectively, control electrodes I5 and I6, respectively, and cathodes I'I and I8, respectively. The multivibrator is of conventional form and has operating current supply circuits which include a suitable-source of potential I9 whose negative terminal is grounded and whose positive terminal is connected to the anodes I3 and I4 through anode resistors 20 and 2|, respectively. The cathodes II and I8 are connected to ground through resistors 2'I :and 28 respectively. The control electrode I5 is connected to ground through a resistor 22 and a portion of a resistor 24 and the control electrode I6 is connected to ground through a resistor 23 and the same portion of the resistor 24. These resistances provide a suitable bias potential for the control relectrodes. In order to cause the discharge devices tooperate in lmultivibrator fashion, a condenser 25 is connected between the control electrode I5 and the anode I4 and a similar condenser 26 is connected between the anode I3 and the control electrode I6.

As is well understood, the action of the multivibrator illustrated in Fig. 1 is to produce periodically substantially square pulses across the resistances 21 and 28. In the illustrated arrangement, the time constants of the discharge devices are chosen such that the ratio of the Width of the positive pulses on the resistance 28 to the width of the negative pulses on the same resistance is the reciprocal of the number of multivibrators. Therefore, in the illustrative example the positive pulses are approximately 20% of a full pulse cycle since five signals are to be transmitted. In other Words, the negative portion of a complete pulse cycle is four times as long as the positive portion. The repetition rate of the pulses may be adjusted to a limited extent by means of the variable resistor 24. Pulses of opposite phase appear across the resistance 21 as indicated `onthe drawingg The positive pulses appearing "onithresistance 28 are impressed across a differentiating circuit comprising a capacitor 30 and a resistance 3l. The diierentiated pulses are thenaappliedito a width modulator and limiter 32. HThere is shown a pair of electron dischargedevices1 33=fandii3ll having anodes 35 and 36, respectively; control electrodes 31 and 38, respectively, and cathodes 39 and til, respectively. The-anodes are-con nected to a source of positive potential 4l through anode resistors 42 and vt3, respectively."The negative terminal of thefsource or battery Lil is grounded. vThe cathodesii-aidlare l`c'orinected together Jar'id' @rounded through a resistance llt.

The pulses"areiinpressedupoirthelcontrol ielectrode 31 andi-the? signals'ffrdm aisuitalblesourcelof audio signal vol-tage' ti-arel'fnnpressed uperyilthe control electrode'ilasi/"by imea'ns-of a cupling condenser y46. t-ll'he controllectrode "-38f is 'adjustably connectedto aepintlothe 'resistance M through a'resistanfc- 41. l increase Vin' -volta'ge appearing on the control electrode 38causes -an increase of 'our-rent throighthel device-34. The resultingincreasedvltagedrbp'facrossithe resistance 44 r-aises the=potexfitlalfY .the'cathode 39-a1`f1d therefore the dischargefdvlcBSfclips the pulses impressed on 'l the" control electrode Y31- at a' Vlevel determinedby thesigriaPi-ipressedon the control electrode 38.

In orderto lchangerr the Ares'ultingItriangular pulses into substantiallyisq'u'ar"pulsesftheclipped` triangular pulses- 'are 'fiinpressed'upon-'- a limiter which may be in'th frmofanelectrorr discharge device -358 havingan anode RM1; controlelectrodez and a cathode53.l'I'l1elliiniter fif-isf-'biased-fby means of a resistorlfonnectedetweenthe cen-l trol electrode--and'-g1'ouiid and ar'esisto 155 'connected between'fthe o'athdlandfground)and a variable resistor 56 eonncted-'b'etWee-the"positive `terminalo'i'lthe source l-'aiidthe cathode in order to adjust theiclippihg*levelofdevice'EllY whereby theV triangular uls'esl iaip'peaniin- 'the anode circuit 'of 'thee-limiter as width modulated, constant intensity pulses.

These pulsesifare employed to'"rn-idulateSinY a suitable modulator Eiftl'ieicarrier?frequencyy produced in a suitable mastencs'illa'torindicated 'by the numeral 51, and thernodulatedlcarrier-is then impressed uponian antennNdirectly oi'- through a suitable power amplifier-Sill.

' InA order to triggertheisecond'iiltivibratorso that the pulsesproduced1` therein' will' immediately follow upon I the terliiiriationlf'offthd pulses lfrom the rst multivibrator-50Min tether Words; so'that initiation of a positive pulse by one multivibrator is synchronized withithelterniinlatinio a positive pulse in the preceding multivibrator! there Lis- -provided ai buier. stage'- Sil*- iivhichf-f-rn'ayincludev an electron dischargef "de'vic'BZ offA the5 pentode'type having an anode f6 3'foontrolele'ctrdes Et-64a and 64b and; cathode 65. The Rzathodeislnormally biasedf sufciently'positive lto maintairifthe --discharge device A:62 normallyfinopefative. For i'this purpose the cathode 65 is connected to a source of positive :potential througlr-afsuitable resitance 65a and is alsoconnected-to grom'xd-'ithrou'gh'af '4 suitable resistance 65h. The anode 63 is connected to a source of positive potential through a resistor 66. The negative pulses appearing across the resistance 21 of the multivibrator It are impresssed upon the control electrode 64 of the discharge device 62 through a diiferentiating circuit .comprising a condenser 68 and a resistor 69. As a result, 4the negative' p'ulsesrl appearing on the resistance 21 are 4differentiated and the short duration, relatively high intensity positive pulses appearing in the output of the differentiator cause the discharge device 62 to conduct only for a short synchronizing interval at the terminai tion of each-negative pulse across the resistance '21. As iswell understood the anode potential of the'discharge device 62 is decreased during the conduction period. Accordingly, a short duration negative pulse appears in the anode circuit and these negative pulses are applied to the control electrode of the nextlmultivibrator discharge device, as, for example, 13a, .by means of a coupling'capacitor 61. These negative pulses are used to synchronize or'trigg'er the'next multivibrator l3a.

The appearance of l the` positive`v pulses' in Athe discharge device l2a`1of 'thernultivibrator Illa causes positive pulses to be'impressed by the pulse modulator and limiter 32a on the modulator 58 'in the same manner as described 'above except that the pulses occur one fifth of a-cycle later intime.

Similarly, the rmultivibrat'o'rslb, 100,' and I0d are triggered in succession toproduce substantially square pulses in themodulator=58. The start of the negative' pulses in multivibrator'ld triggers multivibrator'lll 'and-"thercycle is' repeated.

The'above sequenceis illustrated graphically in Figs 2, 3 and 4. In Fig; 2 there is shown the'order in which pulses occur in the"various'multivibra tors. Thus the pulses 'at a'irFig. 2are those developed in multivibrator I0 and the pulses indicated by letters b, c, d, Vand e 'are those 'developed in the multivibrators 10a, Wb, 'Ille rand kllld vrespectively. In Fig. 3 there' is shown'the appearance ofthe pulses a, b, c; d, 'and e after they have been Width modulated. The Width modulated pulses should be appreciably narrower than the timing or synchronizing pulsessoithat the receiving means may accurately separate and detect the desired pulses. In Fig. 4` there is illustrated the appearance of the Width modulated pulses after they have been combined andlas they areimpressed on the modulator. In'e'ach of Figs'. 2,'- 3 and 4 the time scale, taken in the horizontal direc tion, is the same so that the-positions lof the pulses can be directly compared.

A receiver suitable for receiving and distin guishing betweenthe'pulses-emitted from a transmitter such as that shown in Fig. l is illustrated in Fig; 5. The receiver preferably employs a Wide band xed frequency tuner and 'detector as'indicated `by the numeral 1t. Superlieterodyne ope eration need not he used since variable frequency operation is not necessary. There is employed a multivibrator 1l, which has av free running frequency slightly belowthe frequency employed in the transmitter. The lreceiver multivibrator 1| is synchronized by everyfth pulseof the transmitter. The multivibrator -supplies pulses to a pedestal injector -12 Which'passes 4onlythe pulses corresponding' to the particular audio channel which synchronizes' lthe vl"multivibrator The' pulses vmay then` be-integ'rated in a suitable integrating circuitl and then passed to a'suitable audio amplifier F14 vand 2loudspeaker`15.

The shapes and nature of the 'pulses are indicated at various points in the circuit.

:The pedestal injector comprises a pair oi electron discharge tubes lil and 'il having anodes 'I8 and 79, respectively, control electrodes 8@ and 3l, respectively, and cathodes .32 and 83, respectively. The cathodes are connected together and grounded through a resistance Sil. The detected pulses are impressed upon the control electrode Bil as by means of the coupling capacitor t5. The positive pulses from the multivibrator 'il are irnpressed upon a limiting device cil which is biased to pass the negative pulses. The negative pulses interrupt conduction in the electron discharge device ll. The resistance Sill and the discharge devices l5 and l? are so chosen and arranged that when device il is conducting the voltage drop across the cathode resisto-r de drives the cathode potential of the discharge device "it so positive that the positive pulses appearing on the control electrode lill are insufficient to cause conduction of the discharge device l5. However, when the conduction of the discharge device 'l'lis interrupted, its plate current ceases to flow through' the resistance 84, the potential o the cathode 82 drops, and the discharge device 'le is rendered conductive on the positive detector impulses. In other Words, the injector operation is equivalent to injecting into the discharge device 'l5 or impressing on electrode Sil a positive pulse occurring in time simultaneously With every iifth pulse of the detector output and as a result every rlfth pulse is vtransmitted to 'the integrating circuit. This integrating circuit produces a signal Whose intensity' varies as the pulse Width oi the incoming signal varies. Thus the discharge device ld isarranged so that its anode voltage varies only when a signal voltage appears on its grid and pulses from the multivibrator imultaneously appear, on its cathode. Means is provided for selecting any one of the channels. ln the forni of my invention shown iig. 5 this means taires the form or" a normally closed switch or push button Selection of any one ol the channels may be obtained by momentarily opening the or oper t' push button w-N r the detector c ut. During the the circuit between the detector and the multivibrator is the multivibrator is iree runnin`cr and therefore at a slightly lower rate than the repeti` tion rate of the incoming pulses. When the t i or push button reclosed, the multiator synchrcnizes vf he pulse which is appearing in the detector output at that time. Therefore by opening the circuit for the propel' length ci' time any channel may be selected.

From the above description it is seen that a very simple form of receiver may be employed because variable tuning elements are unnecessary and e. single push button may be employed for selecting the desired program or audio channel. While I have illustrated a system employing five audio channels, any number of channels may be employed. Several groups or" channels may be provi-ded in any receiver by providing a second of frequencies and suitable switching means for selecting the desired band.

rThe xed tuning arrangement makes it possible to obtain high selectivity Wide band operation with sharp cut oli at the edges of the band. There are no critical adjustments either in the transmitter or receiver and accordingly very simple and inexpensive circuits may be used throughout. The fact that a number of audio 6 channels can be provided in the space of one frequency band makes it possible to provide ample guard bands on each side of the assigned frequency band in which case even the sharp cutoi requirements at the edges of the band now imposed by governmental regulations, may be` dropped. g

in Fig. 6 is illustrated a modification of the receiver shown in Fig. 5. is provided in which a separate push button or switch is used for each audio channel in order to remove any degree oi chance or guesswork in locating a desired channel. There is illustrated in Fis'. 5 a switch Slt which is arranged selectively to engage one of a plurality of switch points 9| to 95, inclusive, each of the switch points being connected to a multivibrator so that the injector can be connected with the multivibrator corresponding to the desired signal. The multivibr tors may be connected to the detector output by a suitable integrating circuit or band pass filter as indicated by the numeral lili. With such an arrangement it is necessary to make at least one p ilse in each group of the transmitted pulses different from others in that group in order to synchronize one of the receiver multivibrators with the proper transmitter multivibrator. Once this selection made the multivibratorsmay trigger eachother. The difference may be obtained by providing for a greater pulse width than normal, a greater than normal amplitude, or a frequency deviation into a different band. By such means crm 'f the channels may be always determined.

While l have shown and described a particular embodiment or my invention, it will be obvious to those slr' led in the art that changes and modications may be made Without departing from my invention in its broader aspects, and I, therefore, in the appended claims to cover all such changes vand modications as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a multiplex radio communication system, a transmitting station including a plurality of pulse generators having substantially the same predetermined repetition rate, each of said pulse generators producing a group of spaced apart pulses, means utilizing each of said groups of pulses to synchronize the generator of another of said groups of pulses in successive time relation, means for modulating a characteristic of the pulses of each of said groups in accordance with a desired signal, and a receiving station including a. receiver pulse generator having substantially said predetermined repetition rate, means utilizing a selected group of said modulated pulses to synchronize said receiver pulse generator with said selected group of pulses, means maintaining said receiving station normally inoperative to translate said modulated pulses to its output, means utilizing said receiver generated pulses to render said receiving station periodically operative to translate only one group of said modulated pulses, and means for demodulating said one group of pulses to reproduce a signal.

2. In a multiplex radio communication system, a transmitting station including a plurality of multivibrators each having substantially the same predetermined repetition rate, each of said multivibrators providing in its output circuit a group of spaced apart substantially rectangular pulses, means utilizing the output of each of said multivibrators to synchronize 'anotherl of said multi- A more elaborate system i vibratorsin successive` time ,relation tlierewith,y

saidfreceiver pulse generator With said 'selected group of pulses, means maintaining saidreceivingstation normally inoperative to translatefsaid modulated pulses to its output, means utilizing the-output of said receiver pulse generator to render said receiving station periodically operative to translate only one group of Asaid modulated pulses, and means responsive to said one group of pulses to reproduce a signal.

3. In a multiplex radio communication system, a rst station including means for transmitting a plurality of groups of signal modulated periodic pulses of radio frequency energy spaced apart in successive time relation, each of said groups of pulses having substantially the same predeterminedrepetition rate and being modulated in accordancewith a desired signal, a second ,station including a plurality of multivibrators corresponding in number to the number of said groups of pulses, each of said multivibrators having substantially said predetermined repetition rate, means utilizing the output pulses of each of said multivibrators to synchronize another of said multivibrators to produce output pulses in successivetime relation, means utilizing one of said groups of transmitted pulses to synchronize one oisaid multivibrators with one oi said groupsof pulses, and means` for selectably rendering said multivibrators ,operative to render said second station responsive tolonly a selected oneof said groups oi-modulated. pulses.

4., 111 .-a .multiplex radio transmission system; a.y transmitting station including a plurality of--pulse generators having substantially the same prede,- y. terminedrepetition, rate, each of said pulse gen-H ofwsaid modulatedrpulses-.iandvmeans .for vdemodu- 8 eratorsfpnoduoiug faigroup; ofv` spacedapart and substantiallyrectangular periodic pulses, means utilizngLeaoh-of saidgr-Oups ,ofl rectangular pulses. tosynchronizettlle generator of `another of said grups of :pt11Ses,-insuccessive time relationtherewith',fmeansfonderivng lfrom each 0f `said groups` trol1ing; the potential of another of said electrodes inA accordanceWithfaedesired signal.

5.' In afradio ,communication system, a pluralityyofgfpulse generators having substantially the same repetit-ionrate;eachof said pulse generators V,vprodricirlgf-La@groupsof, spacedapart pulses, means utilizingyeach'off-,said `groupsof pulses to synchronizeithev-generator of-'another of said groups of,pulses-dn-fsuccessive-ti-me relation, means for modulatinga:characteristic,l of the pulses of each .oi- 'saCL :groups-xim-.aocordance fwith a desired signal, `andra receiving'gstation:including a receiver pulsefgenerator ,fhaving'substantially said repetition'yrate,y meanss-:utilizngg'a selected group ,of said modulated pulsesftosyncllronize `said receiver `pulsefgenerator-vvithsaid seleotederoup 0f pulses,

means. maintaining:saidxreceiving station normallyginoperative tof@ translate said modulated` pulses to its eoutputameans `:utilizing said 4receiver generated pulsesxto k:render ,said receiving 'stationl lDemiodioallyppelettive-:to translate `*only one. group lati-ngsaidfone,sgroupof .pulses to reproduce a desir-edsigvnal.,y

EVERLHARD H;- Bi BARTELINK.

REFERENCES .CITED The@following-references -are of record in the le zof--this patent:

STATESv PATENTS Number Name Date 2,262,838 Deloraine et al Nov. 18, 1941 2,272,070 Reeves Feb. 3, 1942 2,418,116r Grieg` Apr. 1, 1947 2,429,608: .Chatteriea et al. Oct. 28, 1947 

